Let me address your question on the JD side. In the early 60's they made the 14t and the 214t. Best just to stay away from these as parts are getting pretty hard to get any more. Late 60's was the 24t and the 224t. If they are in GOOD condition, shed kept and taken care of, the 24t is fine for the little bit you want to do, and the 224t will do a whole lot more than you need, but is a fine piece. There are some basic engineering differences between them. The 24 was the economy model, and the 224 was the professional model at the time. Next in the early 70's came the 336 and the 346. 336 is still a journeyman baler. Parts readily available, good capacity, sound machine. 346 was a few more stocks per minute, a wide pickup, squeezer doors in the chute, and 6 hay dogs instead of 3 like the 336. 336's can range from 500 to as high as 4000 of a really clean great unit. 346's range from 1500 to 6000. There are still thousands of these baler still working out in the field.
As to the one that has been sitting outside for a few years. RUN IN THE OTHER DIRECTION!!!!!! You are likely bitting off much more than you can handle. Especially if it was left out side with hay or straw in it. The rust will be massive and extremely damaging to what is left of the baler. If you had lots of experience working on them and you got if for a few hundred not thousand, maybe okay.
As to the difference in hay feeders on JD vs NH. JD uses the auger behind the pick up, and NH uses the feeder forks. Both work, but the operators ability is more important. Main advantage to the NH forks, you can bale corn fodder with it, but not with the JD auger.
Keep looking, you will find something, but you will likely not find it in time to do you much good this year. Set your sites on next year and spend the winter getting the baler ready. If you get a JD and need info or help with it feel free to ask, and I will do what I can.